1. Technical Field
The present invention relates generally to the field of tie down devices, and more particularly to tie down straps used with ratchet devices.
2. Description of Prior Art
Tie down devices are well known in the art, as are tie down straps used with ratchet devices. Typical tie down strap/ratchet devices employ a substantially inelastic strap and a ratchet take-up device, with a first engagement device located at the distal end of the strap and a second engagement device located proximate to the ratchet. The engagement devices are typically hooks. The strap is taken up by the ratchet and wound about a drum, which shortens the effective length of the strap. Gearing in the ratchet prevents the drum from counter-rotating, thus maintaining the strap length under tension. A release mechanism built into the ratchet disengages the gearing and allows the strap to be unwound from the drum, lengthening the effective length of the strap. In use, the strap is placed over the object or objects to be tied down, the engagement devices are engaged with fixed objects, then the ratchet is used to take up the slack in the strap until the strap is taut over the object or objects intended to be secured. This configuration provides a practical device for securing differently sized objects, since the length of the strap can be as long or as short as needed, within its physical constraints.
While the above-described tie down strap/ratchet device adequately secures a stationary load, if the load is jostled during transport even slight relative movement of the object or objects being secured can result in a slackening of the tension of the strap. See FIGS. 2A-2C. Since the strap is substantially inelastic, any slack introduced to the strap remains and presents a danger of the load becoming less secure. Further jostling may introduce ever more slack to the strap until the load is no longer secured.
Another common tie down device uses an elastic elongate cord having an engagement device at each end. This is typically known as a bungee cord. A bungee cord is used by being placed over the object or objects to be tied down, then the engagement devices are engaged with fixed objects. Because the length of the bungee cord is less than the distance between the fixed objects, the cord is stretched over the object or objects intended to be secured, and the tension in the cord provides the securing means.
While the above-described bungee tie down device is capable of overcoming slack introduced through jostling of the load, it also has disadvantages. Because the bungee cord is of a fixed length, for any given load only a specially sized bungee cord will be adequate. This necessitates multiple bungee cords for different sized loads. Also, since the entire length of the bungee cord is elastic, even a taut bungee cord presents an unwanted amount of stretch. Thus, where slight jostling might not have created movement in a load secured by an inelastic strap, that same degree of jostling will, even if only temporarily, allow movement in the load. While the bungee cord will immediate retract to take up the slack, the total amount of movement of the load may be unacceptable and eventually result in dangerous shifting of the load.
The foregoing illustrates that there is a need in the art for an improved tie down device which incorporates the benefits of both typical tie down systems while avoiding their disadvantages.
It is therefore an objective of the present invention to provide a tie down device that is suitable for securing a load.
It is a further objective of the present invention to provide a tie down device that has a changeable effective length so that it may be used on different sized loads.
It is yet a further objective of the present invention to provide a tie down device that has a strap which is substantially inelastic for most of its length to minimize movement of a secured load.
It is yet a further objective of the present invention to provide a tie down device that has a strap which is substantially elastic for a short portion of its length to allow for automatic re-tensioning of the strap across a load which has shifted slightly.
It is yet a further objective of the present invention to provide a tie down device that is inexpensive to manufacture.
It is yet a further objective of the present invention to provide a tie down device that is easy to use.
Other objectives of the present invention will be readily apparent from the description that follows.